The status of the New START treaty with Russia remains in question as Congress nears the end of its session. Here's a primer on what the treaty is and the politics involved.

As Congress races to the finish of its lame-duck session, one of the last pieces of business is the status of the New START treaty, the latest bilateral effort by the United States and Russia to reduce strategic weapons. President Obama and Russian President Dmitry Medvedev signed the treaty April 8 in Prague, but it requires 67 votes to win approval in the Senate.

What is the treaty?

The New Strategic Arms Reduction Treaty is the latest incarnation of efforts between the United States and Russia to cut back on nuclear weapons. Those efforts go back to the late 1960s, but the most recent steps include START I in 1991, followed by START II and the Moscow Treaty in 2002.

What does New START do?

According to the White House, the latest treaty calls on the parties to limit their nuclear warheads to 1,550 within seven years, a ceiling that would be 74% lower than allowed in START I and 30% down from the Moscow Treaty. New START also limits the number of missiles and other delivery systems of warheads to fewer than half the number allowed START I.

The treaty includes verification requirements including on-site inspections and data and telemetry exchanges.

What is the administration's position for the treaty?

President Obama has argued that decreasing the danger from nuclear weapons is a key plank of his and every previous administration, whether Democrat or Republican. Six Republican former secretaries of State have been among those to have endorsed the proposed treaty.

In addition, Obama has argued that approval is needed to help reset the U.S. relationship with Russia and to provide a common platform of trust so that Russia continues to help on such tough policy issues as limiting Iran's nuclear ambitions and the war in Afghanistan.

What has been the opposition arguments?

There are two different streams of opposition, from Republicans in general and from the GOP in the Senate.

Republican senators, led by Arizona's Jon Kyl, say they can't support a reduction in U.S. nuclear efforts unless there is more attention paid to modernizing the forces and the infrastructure.

In response, the Obama administration has upped its commitment to modernization, saying it will spend more than $85 billion over the next decade, an increase of more than $4 billion from its first proposal. Most of the new money would go to designing and building processing plants at the Los Alamos complex in New Mexico and at the Oak Ridge complex in Tennessee.

Republicans said they welcomed the increase, but they said too little, just $10 billion, would go to weapons. The administration disputes the number.

What are the other arguments against the treaty?

Among other Republican objections are that the treaty would limit national-security interests by hampering U.S. efforts on missile defense, failing to address tactical nuclear weapons, and that it is weak on verification.

The main thrust of many GOP complaints and goes to the idea that somehow the Russians are getting the best of the negotiations and that U.S. security is jeopardized. The United States is further along in missile defense systems than Russia, so for Republicans, limiting those systems would hurt the United States. The same logic applies to tactical weapons, since Russia has more of them, though their actual value in combat is the subject of debate.

The administration counters that the treaty has nothing to do with missile defense systems. "The treaty does not contain any constraints on testing, development or deployment of current or planned U.S. missile defense programs or current or planned United States long-range conventional strike capabilities."

Nor does the treaty deal with tactical as opposed to strategic offensive weapons, which are designed to be delivered by missiles to large targets. Tactical weapons are smaller and are generally limited to battlefield use. The current thrust of limiting the dangers of nuclear war start with an agreement on larger weapons before moving on to the smaller, the administration argues.

On verification, Obama has frequently quoted conservative icon Ronald Reagan, who often cited a Russian adage: Trust but verify. Obama argues that without the treaty, the United States would lose on-site inspection and be unable to verify whether the Russians are indeed doing what treaties require them to do.

What are the politics?

Top Republican senators argue that there may not be enough time left in the lame-duck session to study the treaty and that it could be put off until the new Congress is sworn in in January. Republicans have said they will not consider any measure until the tax-cut extensions are resolved.

The Obama administration has made ratification a top priority and is optimistic that the treaty will get a vote. But some Republicans would certainly be happy to deny the administration any appearance of a victory on the foreign front after forcing serious compromises on the tax issue.